US4033176A - Pocket-sized, direct-reading ultrasonic thickness gauge - Google Patents

Pocket-sized, direct-reading ultrasonic thickness gauge Download PDF

Info

Publication number
US4033176A
US4033176A US05/595,060 US59506075A US4033176A US 4033176 A US4033176 A US 4033176A US 59506075 A US59506075 A US 59506075A US 4033176 A US4033176 A US 4033176A
Authority
US
United States
Prior art keywords
time
gate
pulse
signals
variable
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US05/595,060
Other languages
English (en)
Inventor
Frederick L. Eberle
Bernard Ostrofsky
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
BP Corp North America Inc
Original Assignee
BP Corp North America Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by BP Corp North America Inc filed Critical BP Corp North America Inc
Priority to US05/595,060 priority Critical patent/US4033176A/en
Priority to JP51082834A priority patent/JPS5215374A/ja
Application granted granted Critical
Publication of US4033176A publication Critical patent/US4033176A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B17/00—Measuring arrangements characterised by the use of infrasonic, sonic or ultrasonic vibrations
    • G01B17/02—Measuring arrangements characterised by the use of infrasonic, sonic or ultrasonic vibrations for measuring thickness
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/04—Analysing solids
    • G01N29/07—Analysing solids by measuring propagation velocity or propagation time of acoustic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/028—Material parameters
    • G01N2291/02854—Length, thickness

Definitions

  • This invention relates to an electronic time base measurement circuit and in one of its aspects to an electrical circuit for performing such measurements in an ultrasonic inspection system.
  • a piezoelectric crystal In ultrasonic flaw-detector and thickness measuring instruments, a piezoelectric crystal (transducer) is placed on or near the surface of the material whose integrity or thickness is to be measured. In order to insure effective coupling between the transducer and the surface, the space between may be filled with an acoustically transparent material, i.e., a material having a small amount of accoustical attenuation such as water or oil.
  • the output of a pulse generator consisting of short duration voltage pulses, is applied to the crystal.
  • high frequency sound generated by the crystal when it is pulsed passes through the material, is reflected from the opposite surface, and returns to the crystal where the back-reflected sound causes the crystal to again oscillate.
  • the same sequence of events may happen repeatedly and there may be a second, third or even greater number of back-reflections due to the same voltage pulse.
  • the voltage pulse initiating this sequence is called the initial pulse.
  • Ultrasonic pulse-echo thickness measurement apparatus generally consists of a highly damped piezoelectric transducer excited by an ultrasonic pulse generator connected thereto, injects ultrasonic pulses of short duration into a specimen such as a plate metal, to determine the thickness D thereof. After entering the specimen, the ultrasonic pulse is repeatedly reflected back and forth between the parallel surfaces of the specimen separated by the dimension D until its energy is dissipated. During this reverberation process, piezoelectric transducer which also acts as an ultrasonic receiver, generates a short voltage pulse each time the ultrasonic pulse strikes upon the specimen surface to which the piezoelectric transducer is coupled. Thus, following the emission of the initial excitation pulse, a sequence of electrical pulses is produced by the piezoelectric transducer. The time interval T between two consecutive pulses of this sequence is equivalent to the specimen thickness according to
  • V L represents the longitudinal ultrasonic wave velocity in the material of the specimen.
  • the longitudinal ultrasonic wave velocity is usually constant within a wide range of ultrasonic frequencies and the specimen thickness D can be determined by measuring the pulse period T or its reciprocal.
  • the time interval between the initial pulse and a back-reflection or between various reflection pulses can be determined by displaying on an oscilloscope the sinusoidal voltage across the crystal corresponding to the initial pulse and back-reflections. Thickness of the material being tested was then read on the horizontal or time axis of the oscilloscope.
  • a more recent development is the direct-reading instrument which displays thickness measurements directly on a meter or on a digital read-out display.
  • a constant current source is used to charge a capacitor at a linear rate with respect to time.
  • the constant current source is gated-on by the initial pulse and gated-off by the first back-reflection.
  • the charge on the capacitor is, therefore, dependent on the elapsed time between the initial pulse and the first back-reflection which, in turn, depends on the thickness of the material.
  • the charge on the capacitor at any time is indicated on a meter or a digital-type display.
  • the readout, whether meter or digital-type, is calibrated directly in inches.
  • Both the oscilloscope and direct-reading type instruments require considerable electronic circuitry and, as a consequence, have a large physical size. Both of these instruments are also relatively expensive.
  • This invention provides a simple and novel method and apparatus for measuring the elapsed time between two consecutive signals and is not limited to ultrasonic testing. In one specific embodiment, it provides a method and apparatus for measuring the elapsed time between an initial pulse and the first back-reflection or between various reflection pulses in ultrasonic testing. The apparatus is less expensive and much smaller than the instruments currently in use. This invention provides an accurate ultrasonic thickness measuring device which is made from simple, inexpensive electronic components and which can be easily hand held.
  • This invention provides a method and apparatus for measuring the time interval between two or more sequential signals.
  • One particular application is measuring the time interval between pulses in non-destructive ultrasonic testing.
  • a time-variable gate is used to effectually span the time interval between signals, the interval of the gate corresponding to the time interval between signals.
  • the method and apparatus of this invention is based upon the use of a time-variable gate which can be implemented a number of ways.
  • a time-variable gate controls the sending of the response signal so that the response signal will be sent corresponding to a discrete number of received signals.
  • two or more sequential signals are received and then amplified by an amplification means.
  • the ON/OFF condition of the amplification means is controlled by a time-variable gate so that the amplification means is switched ON for a time just sufficient to amplify the received signals.
  • the time during which the gate switches the amplification means ON corresponds to the elapsed time between the signals.
  • This method and apparatus provides a simple and novel method of measuring the elapsed time between the initial pulse and the first back-reflection in an ultrasonic thickness measuring instrument:
  • a piezoelectric crystal is pulsed in the usual way.
  • the resulting initial pulse and associated back-reflections are amplified and fed to a pulse counter.
  • the output of the counter is a current, which is displayed on a meter.
  • the amount of current corresponds to the number of input pulses to the counter.
  • a variable-width square wave generator supplies a square wave, which gates the amplifier ON from a normally OFF condition.
  • the duration of the square wave can be varied by means of a potentiometer so that the amplifier is gated-on for only the time necessary to amplify the initial pulse and first back-reflection.
  • the duration of the square wave then corresponds to the elapsed time between the initial pulse and the first back-reflection. Since the potentiometer controls the duration of the square wave, it can be calibrated directly in units of time or material thickness.
  • the most common means of generating square wave is through use of a multivibrator which can develop a wave, thereby switching a piece of equipment ON or OFF in less than a few milliseconds, preferably less than 1/10 of a microsecond.
  • a multivibrator is essentially two stages of resistance-capacitance-coupled amplification with output connected to input. Usually the coupling is between the plates and the grids, but cathode coupling may also be used. Any casual disturbance in the potential of the first grid is amplified and reversed in polarity by the two stages. The two reversals of polarity produce, at the first grid, a signal of large magnitude and the same polarity so that initially assumed. Consequently the potential of the first grid is rapidly shifted, by cumulative action, in the direction of the first disturbance. If the disturbance was negative, the first stage becomes non-conducting or is "cut off", usually in a few millionths or thousandths of a second. In this case, the plate of the first stage is raised in potential, driving the grid of the second stage sharply positive and holding the second stage at full conduction. If the initial disturbance was positive, the first stage reaches full conduction at once, while the second stage is cut off.
  • the waveform taken from either plate has a rectangular shape in the upper, positive portions and an exponential shape in the lower, negative portions. If both coupling circuits have the same time constant, the duration of positive and negative portions in the same (symmetrical multivibrator). By suitable choice of the time constants, it is possible to vary the relative duration of the two portions and, in effect, to produce short, sharp pulses separated by longer quiescent intervals.
  • FIG. 1 is a block diagram of an ultrasonic thickness measuring device employing the disclosed apparatus for measuring time intervals between sequential signals.
  • FIG. 2 is a schematic diagram of the same device.
  • the output of a unijunction pulse generator 1 is used to trigger a SCR (silicon controlled rectifier) pulser 2.
  • the output of the pulser 2 causes the piezoelectric crystal 3 to oscillate at its resonant frequency. Bursts of crystal oscillation, due to both the pulser and the back-reflections from the sample 4, are amplified and rectified in the amplifier 5 and detector 6 stages, respectively.
  • the amplified and rectified signal is fed to the pulse counter 7 which converts the number of bursts of crystal oscillation per second to an equivalent current which is displayed on a meter 8.
  • the pulser pulses the piezoelectric crystal and causes it to oscillate, it also starts the variable-width square-wave generator.
  • the output of the variable-width square-wave generator 9 is used to gate the amplifier 5 ON from its normally OFF condition.
  • the width of the square-wave is adjusted by means of a potentiometer so that the amplifier 5 is gated ON for only the minimum time necessary to amplify the crystal oscillation burst due to the pulser (initial pulse) and the first back-reflection. This is indicated on the meter 8 as a current twice as large as is obtained from the initial pulse alone. Since the elapsed time between the initial pulse and the first back-reflection is directly proportional to the thickness of the sample, the potentiometer in the variable-width square-wave generator can be calibrated directly in inches.
  • the pulse generator uses a 2N2647 unijunction transistor 50 as a relaxation oscillator.
  • a 10,000 ohm, 1/2 watt carbon resistor 51 and a 0.022 microfarad Mylar capacitor 52 establish a pulse repetition rate of 360 pulses per second.
  • a 270 ohm, 1/2 watt carbon resistor 53 functions as a temperature compensating resistor.
  • pulse generator output resistor 54 a 27 ohm, 1/2 watt carbon resistor, a positive pulse is provided for triggering the 2N4149 silicon controlled rectifier (SCR) 55.
  • SCR silicon controlled rectifier
  • the variable-width, square-wave generator is triggered by the SCR pulser 55.
  • Pulser load resistor 56 and pulser to transducer coupling capacitor 57 are provided by a 3300 ohm, 1/2 watt carbon resistor and by a 0.002 microfarad disc ceramic capacitor, respectively.
  • transducer 58 which is a 5 megahertz lead metaniobate crystal.
  • Transducer tuning inductor 59 and transducer tuning resistor 60 are provided by a 0.7 microhenry inductor and a 2.2 ohm, 1 watt carbon resistor respectively.
  • the above described pulse generator and SCR pulser also provide a pulse for triggering the variable-width square-wave generator.
  • the pulser is connected to the square-wave generator through coupling capacitor 61 which is a 500 picofarad disc ceramic capacitor.
  • the variable-width square-wave generator is a monostable multivibrator consisting of an Motorola MC 74121F integrated circuit 62. Connected thereto, a 0.022 microfarad mylar capacitor 63 and a 2000 ohm, linear taper potentiometer 64 are used to determine the width of the square wave. Use of the potentiometer permits the width to be varied from 0 to approximately 20 microseconds.
  • a 1.0 millihenry inductor 65 is provided for shaping the gate signal.
  • Signals received by the transducer 58 are sent to the amplifier 71 through a coupling capacitor 66 and a coupling resistor 67 which are a 0.001 microfarad, mylar capacitor and a 1000 ohm, 1/2 watt carbon resistor, respectively.
  • a 0.01 microfarad mylar capacitor serves as R. F. bypass capacitor 68.
  • Resistors 69 and 70 are voltage dividers consisting of 1000 ohm, 1/2 watt and 2200 ohm, 1/2 watt carbon resistors, respectively.
  • the output of the variable-width square-wave generator 62 is applied to the amplifier 71 through gate signal shaping inductor 65 and controls the ON/OFF condition of the amplifier.
  • R. F. amplifier 71 is an RCA CA 3028A differential amplifier integrated circuit.
  • the amplifier circuit amplifies the oscillations from the piezoelectric crystal when in an ON condition and passes the output through an amplifier output capacitor-inductor circuit comprising a 120 picofarad silver mica capacitor 72 and a 8.5 microhenry inductor with coupling link 73.
  • R. F. bypass capacitor 74 is provided by a 0.01 microfarad mylar capacitor ohm, a 2N1308 transistor.
  • the amplifier output is link-coupled to the base of the detector transistor 75.
  • the detector load resistor is a 1200 ohm, 1/2 watt carbon resistor 76.
  • the detector is coupled to a square wave generator 79 by a 500 picofarad silver mica capacitor 77 and 33,000 ohm, 1/2 watt carbon resistor 78.
  • the pulse counter consists of an MC 74121F monostable multivibrator 79 and a 2N5172 counter transistor 84.
  • Square-wave width capacitor 80 and resistor 81 are provided by a 0.001 microfarad mylar capacitor and a 1500 ohm, 1/2 watt carbon resistor, respectively.
  • the multivibrator 79 produces a single square-wave of constant amplitude and duration. The duration is approximately 1.0 microsecond and is determined by capacitor 80 and resistor 81.
  • the square-wave generator is coupled to the counter transistor 84 by coupling capacitor 82 and coupling resistor 83, which are a 10 microfarad tantalum capacitor and a 1 megohm, 1/2 watt carbon resistor, respectively.
  • Output of the square-wave generator passes to counter transistor 84 and then through counter load resistor 85, a 1000 ohm, 1/2 watt carbon resistor. This signal is displayed on counter meter 86, a 20 microampere microammeter.
  • the output from the unijunction pulse generator 50 is a 3 volt positive pulse occurring at a rate of 360 pulses per second. This pulse triggers the SCR pulser 55 to produce a negative pulse 9 volts in amplitude.
  • the pulser output causes the variable-width square-wave generator 62 to generate a 4 volt positive square-wave.
  • the voltage across the piezoelectric crystal 58 consists of a succession of damped 5 MHz oscillations due to the initial pulse from the pulser 55 and the multiple back-reflections from the sample. After amplification, only the initial pulse and first back-reflection are present. This is because the width of the square-wave gating signal applied to amplifier 71 was adjusted so that the amplifier was gated-on only long enough to amplify the initial pulse and first back-reflection.
  • the signal passes through the detector stage where it is rectified and the RF removed.
  • the signal at the output of detector 75 consists of negative pulses which, after shaping in an RC network, are used to trigger square-wave generator 79 in the pulse counter.
  • the square-wave generator 79 For each trigger pulse, the square-wave generator 79 produces a single square-wave having an amplitude of positive 4 volts and a duration of approximately 1 microsecond. The duration and amplitude of each squarewave is constant and is independent of the shape and amplitude of the trigger pulse. This ensures that, for all samples, the counter transistor 84, which is fed by the square-wave generator, registers the same current reading on the meter for the initial pulse and first back-reflection.
  • the transducer is placed against the sample with an oil couplant between sample and transducer.
  • the time variable gate is slowly opened, that is lengthened in time, until the counter meter abruptly changes from 0 to 5 MA when the initial pulse is gated-in and from 5 to 10 MA with the first back-reflection.
  • the time variable-gate is open to a width or rather time which corresponds to the time between the initial pulse and first back-reflection and the time can be determined by simple calibration of the potentiometer used to vary the time-variable gate.

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Biochemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Acoustics & Sound (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Length Measuring Devices Characterised By Use Of Acoustic Means (AREA)
  • Measurement Of Unknown Time Intervals (AREA)
US05/595,060 1975-07-11 1975-07-11 Pocket-sized, direct-reading ultrasonic thickness gauge Expired - Lifetime US4033176A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US05/595,060 US4033176A (en) 1975-07-11 1975-07-11 Pocket-sized, direct-reading ultrasonic thickness gauge
JP51082834A JPS5215374A (en) 1975-07-11 1976-07-12 Method and device for measuring time interval between at least two signals

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US05/595,060 US4033176A (en) 1975-07-11 1975-07-11 Pocket-sized, direct-reading ultrasonic thickness gauge

Publications (1)

Publication Number Publication Date
US4033176A true US4033176A (en) 1977-07-05

Family

ID=24381550

Family Applications (1)

Application Number Title Priority Date Filing Date
US05/595,060 Expired - Lifetime US4033176A (en) 1975-07-11 1975-07-11 Pocket-sized, direct-reading ultrasonic thickness gauge

Country Status (2)

Country Link
US (1) US4033176A (en, 2012)
JP (1) JPS5215374A (en, 2012)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4947351A (en) * 1988-05-06 1990-08-07 The United States Of America As Represented By The Secretary Of The Air Force Ultrasonic scan system for nondestructive inspection
US4991440A (en) * 1990-02-05 1991-02-12 Westinghouse Electric Corp. Method of ultrasonically measuring thickness and characteristics of zirconium liner coextruded with zirconium tube
CN110500974A (zh) * 2019-08-06 2019-11-26 天津大学 基于改进峰值识别的工件厚度检测方法

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2562450A (en) * 1947-07-05 1951-07-31 Sperry Prod Inc Pulse cutoff device
US3238767A (en) * 1962-12-11 1966-03-08 Manfred E Clynes Ultrasonic pulse-echo system for internal exploration
US3256733A (en) * 1963-02-06 1966-06-21 Air Shields Ultrasonic pulse-echo apparatus for internal exploration
US3262306A (en) * 1962-09-19 1966-07-26 Branson Instr Ultrasonic testing system
US3427866A (en) * 1965-10-26 1969-02-18 Frederick Gordon Weighart Ultrasonic thickness gauge and flow detector
US3690154A (en) * 1969-07-21 1972-09-12 Atomic Energy Authority Uk Apparatus for measuring thickness
US3748895A (en) * 1971-06-01 1973-07-31 Magnaflux Corp Pulse ultrasound thickness measuring system having interrogation control

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2562450A (en) * 1947-07-05 1951-07-31 Sperry Prod Inc Pulse cutoff device
US3262306A (en) * 1962-09-19 1966-07-26 Branson Instr Ultrasonic testing system
US3238767A (en) * 1962-12-11 1966-03-08 Manfred E Clynes Ultrasonic pulse-echo system for internal exploration
US3256733A (en) * 1963-02-06 1966-06-21 Air Shields Ultrasonic pulse-echo apparatus for internal exploration
US3427866A (en) * 1965-10-26 1969-02-18 Frederick Gordon Weighart Ultrasonic thickness gauge and flow detector
US3690154A (en) * 1969-07-21 1972-09-12 Atomic Energy Authority Uk Apparatus for measuring thickness
US3748895A (en) * 1971-06-01 1973-07-31 Magnaflux Corp Pulse ultrasound thickness measuring system having interrogation control

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4947351A (en) * 1988-05-06 1990-08-07 The United States Of America As Represented By The Secretary Of The Air Force Ultrasonic scan system for nondestructive inspection
US4991440A (en) * 1990-02-05 1991-02-12 Westinghouse Electric Corp. Method of ultrasonically measuring thickness and characteristics of zirconium liner coextruded with zirconium tube
CN110500974A (zh) * 2019-08-06 2019-11-26 天津大学 基于改进峰值识别的工件厚度检测方法

Also Published As

Publication number Publication date
JPS5215374A (en) 1977-02-04
JPS6245502B2 (en, 2012) 1987-09-28

Similar Documents

Publication Publication Date Title
US2280226A (en) Flaw detecting device and measuring instrument
US4102205A (en) Method and apparatus for ultrasonic nondestructive testing of workpieces with automatic compensation for the probe, workpiece material, and temperature
US3504532A (en) Nondestructive testing system
US3812709A (en) Stress gage
US2439131A (en) Resonance inspection method
Forgacs Improvements in the Sing‐Around Technique for Ultrasonic Velocity Measurements
US2888824A (en) Ultrasonic thickness gauge
US3423992A (en) Ultrasonic apparatus for measuring thickness or distances
US4134081A (en) Clock circuit for use in pulse-echo ultrasonic defect testing
US4033176A (en) Pocket-sized, direct-reading ultrasonic thickness gauge
Williamson et al. Coherent Detection Technique for Variable‐Path‐Length Measurements of Ultrasonic Pulses
JPS6314762B2 (en, 2012)
Yoḡurtçu et al. An apparatus for high precision measurements of ultrasonic wave velocity
US2889705A (en) Material thickness and deflect testing device
US3348410A (en) Dynamic gain control for ultrasonic testers
US3427868A (en) Ultrasonic device for measuring the thickness of objects
US3604250A (en) Coupling network for an ultrasonic testing system
US3554015A (en) Ultrasonic pulse-echo apparatus
US3153928A (en) Ultrasonic measurement instrument
SU1196751A1 (ru) Способ измерени концентрации газовых включений в жидкости
JPH06148148A (ja) 超音波減衰測定法とそれを用いた材料特性評価法
Gushchina et al. Development of the experimental equipment for measuring the velocity of ultrasonic waves with high accuracy
US3538751A (en) Direct reading ultrasonic thickness gage
RU2034236C1 (ru) Ультразвуковой эхо-импульсный толщиномер
US3115771A (en) Method and apparatus for ultrasonic shearwave inspection